Standing Stone / Menhir

Miscellaneous

You can see this stone outside the Guildhall near Kingston market. It was used as the coronation stone from Edward the Elder in 900AD to Edmund Ironside in 1016 - they were crowned sat on it.
But surely they didn't just pick some random stone from the ground in 900AD? surely it had some 'provenance'? Perhaps someone knows some more about this - or perhaps it's impossible to know now.